A longer delay of up to 45 weeks leads to enhanced immune response after the second dose, researchers found.
A trial by The Oxford Vaccine Group has found that patients who waited up to 45 weeks for their second dose had a heightened immune response.
Having a third dose more than 6 months after the second increased antibodies too.
Oxford Professor Teresa Lambe described it as 'very encouraging news, if we find that a third dose is needed.'
Supply shortages are causing concern in some countries about compromised immunity, and Oxford Professor Sir Andrew Pollard says the results should come as 'reassuring news'
The results on the ChAdOx1 nCoV-19, also known as the Oxford-AstraZeneca vaccine, were released in a preprint today.
Sir Andrew Pollard, Professor of Paediatric Infection and Immunity and Lead Investigator of the Oxford University trial of the vaccine, says, 'This should come as reassuring news to countries with lower supplies of the vaccine, who may be concerned about delays in providing second doses to their populations.
'There is an excellent response to a second dose, even after a 10 month delay from the first.'
Some countries are considering administering a third 'booster' dose in the future.
Studying the impact of a third vaccine dose, the researchers found that antibody titres increased significantly. T-cell response and the immune response against variants were also boosted.
'It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern,' says Associate Professor Teresa Lambe OBE, lead senior author for these studies.
'Here we show that a third dose of ChAdOx1 nCoV-19 is well tolerated and significantly boosts the antibody response. This is very encouraging news, if we find that a third dose is needed.'
Side effects of the vaccine itself were also found to be well-tolerated, with lower incidents of side effects after second and third doses than after first doses.
The team said further research was needed to follow up with study participants who received third doses beyond the period that was part of the initial study.